The present invention generally relates to a test device and method for testing a biological fluid for the presence of certain xe2x80x9cdrugs of abusexe2x80x9d, and more specifically relates to a lateral flow testing device and method for testing for the presence of methamphetamines in a biological sample and the elimination of undesirable cross-reactivity to other substances that may be present in the sample.
Clinical diagnosis relates, in general, to the determination and measurement of various substances which relate to the health or general status of an individual. Physicians, health care workers and the general public as well are concerned about the presence and levels of various substances in body fluids such as blood, urine, and so forth. Among the substances which have been measured in clinical analysis for a long time are glucose, cholesterol, and various enzymes such as amylase and creatine kinase.
Lateral flow testing devices are widely used for detecting of specific compounds, or analytes, in a biological fluid specimen. One or more reagents are striped onto a solid material, such as a cellulose or paper strip, the reagents being selected as necessary or helpful in detection of the analyte in question. A fluid sample, is deposited onto the strip and will migrate, by capillary action, along the strip where the chemical reactions may take place, depending upon the presence or absence of the analyte, in situ.
Devices for testing for the presence of substances-of-abuse, for example, drugs regulated by law with respect to possession and use, by chemical analysis of a biological fluid sample are well known. In the past, methamphetamines have been detected using a number of techniques, including thin layer chromatography (TLC), gas chromatography (GC), and high performance liquid chromatography (HPLC). These methods generally involve chemical extractions of the drugs, complicated procedures requiring highly trained personnel and lengthy assay times. Thin layer chromatography is labor intensive and lacks sensitivity. Gas chromatography and high performance liquid chromatography each of which is also labor intensive, require highly trained personnel to carry out extractions of the analyte from the biological matrix. In addition, gas chromatography normally requires a derivation step.
More recently, competitive binding immunoassays have been developed for testing a biological fluid for the presence of certain substances of abuse, and these provide a preferable alternative to the physical methods described briefly hereinabove. Immunoassay test devices generally include an absorbent, fibrous strip having one or more reagents incorporated at specific zones on the strip. The fluid sample is deposited on the strip and by capillary action the sample will migrate along the strip, entering specific reagent zones in which a chemical reaction may take place. At least one reagent is included which manifests a detectable response, for example a color change, in the presence of a minimal amount of the substance of interest.
A limitation with lateral flow xe2x80x9cdrugs of abusexe2x80x9d testing products based on immunoassay technologies is the potential false positive resulting from the client using over the counter products, such as diet substances or sinus relief medications. These products may contain the active substances ephedrine or pseudoephedrine. Several methamphetamine immunoassay based lateral flow testing products will exhibit undesirable cross-reactivity with this group of sympathomimetic amines. This produces a xe2x80x9cfalsexe2x80x9d positive initial screening result, which typically requires the fluid sample to be sent to a laboratory for further testing and confirmation of the result. The confirmation laboratory may use several ancillary procedures followed by gas chromatographyxe2x80x94mass spectrometry (xe2x80x9cGC/MSxe2x80x9d) analysis in order to address possible cross-reactivity issues. The GC/MS procedure involves chemical extractions of the drugs in question, complicated procedures and requires highly trained personnel.
Pretreatment of a urine sample prior to immunoassay testing in order to reduce the occurrence of false positives has been proposed. For example, U.S. Pat. No. 5,262,333 to Heiman et al., issued on Nov. 16, 1993, discloses a method for determining amphetamine and d-methamphetamines in a urine sample using fluorescence polarization immunoassay techniques. The procedure described in the Heiman, et al. patent includes a step of pretreating the urine sample to eliminate cross-reactivity (i.e. the recognition of compounds other than the desired substance of interest) by preincubating the sample with an aqueous periodate solution having a pH of about 4.5. According to Heiman et al., the described procedure will reduce the occurrence of xe2x80x9cfalsexe2x80x9d positives resulting from cross-reactivity for 1-methamphetamine, and other amphetamine-like compounds, commonly occurring in prescriptions and over-the-counter medications.
U.S. Pat. No. 5,573,955, issued on Nov. 12, 1996 to Khanna et al., describes a method for reducing or eliminating tyramine interference from amphetamine and methamphetamine immunoassays, including pretreating the sample with aqueous tyramine oxidase for a time and at a temperature and pH sufficient to deaminate any tyramine present in the sample. The pretreated sample is then applied to an immunoassay test device.
It would be beneficial to have an easy-to-use, inexpensive, reliable device and method for testing a biological fluid specimen for the presence of certain drugs-of-abuse, without the need for complicated, costly confirmation procedures, and without requiring a pretreatment step to reduce or eliminate potential occurrences of xe2x80x9cfalse positivexe2x80x9d results. The present invention provides such a device and method.
Accordingly, devices and methods are provided by the present invention that are useful for detecting a presence of certain substances of abuse, for example methamphetamine, without presenting cross-reactivity issues to other similar substances that may be present in sample.
Particularly, a competitive inhibition assay test device is provided. The device generally comprises a substrate, for example a nitrocellulose test strip having a sample introduction portion and a drug detection portion. Incorporated onto the drug detection portion is means for detecting a presence of methamphetamines in a sample of biological fluid, for example urine. The drug detection means includes a color particle coupled antibody and an immobilized drug conjugate zone. The immobilized drug conjugate zone is in the form of a line on the strip and is retained through physisorption. When a sample is introduced onto the sample pad, it migrates onto the conjugate pad and solubilizes the coupled antibody. The sample and the color tagged antibody travel down the lateral flow strip and is wicked onto an absorbent end pad which serves to drive the sample through the strip via capillary action. The mobilized colored antibody migrates down the strip toward the drug conjugate line. If the antibody recognizes the drug on the drug conjugate line, a portion of the solution is stopped and forms a colored line. The remainder continues to flow down the strip where another portion interacts with a nonspecific xe2x80x9ctest validxe2x80x9d line. The remainder flows into an end pad connected to the strip. Such methamphetamine test strips as are well known and therefor the details of manufacturing such strips are not included herein.
Importantly, however, unlike conventional methamphetamine test devices, the present device further comprises an additional chemical reagent disposed on-board the substrate strip. This additional chemical reagent provides means for preventing undesirable cross-reactivity caused by the presence of certain active compounds, such as ephedrine and pseudoephedrine, that may be present in the fluid specimen. More specifically, the chemical reagent comprises sodium periodate, applied or striped onto the substrate. The sodium periodate is applied to a portion or zone of the substrate positioned between the antibody zone and the immobilized drug conjugate zone. It has been found that placement of the sodium periodate zone is critical to the effectiveness of the present device. Placement of the sodium periodate zone in a different location on the strip, e.g. prior to the colored particle antibody zone, is ineffective in preventing ephedrine or pseudoephedrine related interference problems.
Advantageously, the present device provides a simple, inexpensive, reliable methamphetamine test strip that will not exhibit so called xe2x80x9cfalsexe2x80x9d positive test results, even when used for methamphetamine screening of an untreated urine specimen which contains ephedrine or pseudoephedrine.